This invention relates to apparatus for measuring the distortion of data signals by means of a counter which, during each element of the data signal, is caused by a counter pulse train to count from an initial value to a final value. A store also used for display purposes stores the counts which occur simultaneously to the edges of the data signals and measuring pulses which are thereby produced. A decoder decodes the stored counts, and a display device displays the decoded counts.
Various apparatus for the measurement of the distortion of data signals are already known which display the distortion on cathode ray tubes. Apparatus of this type are usually employed at data element rates of up to approximately 10kBd. A known circuit arrangement contains a counter which, for the duration of the element, is caused to count from a constant initial value up to a constant final value. When the data signal which is to be measured changes its binary value, the instantaneous count is recorded, for display, into a store. The stored count causes a deflection of the electron beam in the cathode ray tube and the distortion of the data signal can be read off on the screen. Apparatus of this type is not suitable for measuring the distortion at element rates of above 10 kBd, as the individual measured values cannot be seen on the screen of known cathode ray tubes at these element rates.
Furthermore, apparatus is known for measuring the distortion of data signals which can also be used at element rates of up to 100 kBd. This apparatus also contains a counter which, during the length of an element, counts up once from a constant initial value to a constant final value. The outputs of the counter are connected to the inputs of a decoder which is provided with a number of outputs corresponding to the possible counts of the counter. At each output of the decoder is connected a store which is assigned a display store and a luminescence diode. When the data signal which is to be measured changes its binary value, a store is in each case switched from its rest position to its operative position and the associated luminescence diode is triggered via the display store. With this known device it is also impossible to accurately measure the distortion at element rates of above 100 kBd, as there is not sufficient time to decode and store the count. The given limit of the element speed is here determined not by the display, but by the acquisition of the measured value.
An object of the invention is, therefore, to provide apparatus for measuring the distortion of data signals which operates with a high degree of accuracy, even at element rates of above 100 kBd.